Creping adhesives containing polyvinyl alcohol and thermoplastic polyamide resins derived from poly(oxyethylene) diamine

ABSTRACT

An improved wettable creping adhesive comprises an aqueous admixture of polyvinyl alcohol and a water-soluble thermoplastic polyamide resin comprising the reaction product of a polyalkylene polyamine, a saturated aliphatic dibasic carboxylic acid, and a poly(oxyethylene) diamine.

BACKGROUND OF THE INVENTION

In the manufacture of tissue products such as facial tissue, bathtissue, and paper toweling, softness is imparted to the product byadhering the web to a rotating creping cylinder and thereafterdislodging it from the creping cylinder with a doctor blade. In orderfor the creping process to be effective, it is necessary to obtainproper adhesion between the web and the creping cylinder, which isgenerally achieved by the addition of a creping adhesive. Very smallamounts of adhesive are applied per revolution of the creping cylinder.For good creping, an adhesive coating must build up on the surface ofthe dryer and is continuously renewed during each revolution of thedryer as a small amount is removed by the doctor blade and replaced byfreshly applied adhesive. The newly applied adhesive is incorporatedinto the existing coating, which is reactivated by taking on moisturefrom the fresh application. Therefore, rewettability is an importantproperty of a good creping adhesive.

In an effort to seek new and improved creping adhesives, awater-soluble, thermosetting, cationic polyamide resin creping adhesivewas developed as described in U.S. Pat. No. 4,501,640 to Soerens.However, although such a creping adhesive exhibits good adhesion, thethermosetting nature of such adhesives works against rewettabilitybecause after cross-linking (curing) the addition of moisture is nolonger able to soften and conform the coating sufficiently to optimallybond with the tissue web at the pressure roll nip.

Therefore there is a need for an improved method of creping cellulosicwebs which uses a creping adhesive exhibiting improved wettability.

SUMMARY OF THE INVENTION

It has now been discovered that a creping adhesive comprising an aqueousadmixture of polyvinyl alcohol and a water-soluble, thermoplasticpolyamide resin derived from poly(oxyethylene) diamine exhibits improvedwettability and therefore improved performance in the creping process.

In one aspect, the invention resides in a creping adhesive comprising anaqueous admixture of polyvinyl alcohol and a water-soluble thermoplasticpolyamide which is the reaction product of a polyalkylene polyamine, asaturated aliphatic dibasic carboxylic acid, and a poly(oxyethylene)diamine.

The polyvinyl alcohol component can be of any water-soluble molecularweight sufficient to form an adhesive film. Generally, a weight averagemolecular weight of from about 90,000 to about 140,000 is preferred.Polyvinyl alcohol in solid form is commercially available under severaltrademarks such as GELVATOL® (Monsanto), VINOL® (Air Products), ELVANOL®(DuPont) and POVAL® (Kuraray). Suitable commercially available gradeshave a viscosity of from about 13 to about 50 centipoise for a 4%aqueous solution at 20° C. These grades have a degree of hydrolysis offrom about 80 to about 99.9 percent. Those skilled in the art willappreciate that lowering the degree of hydrolysis and the molecularweight will improve water solubility but will reduce adhesion. Thereforethe properties of the polyvinyl alcohol will have to be optimized forthe specific application.

The water-soluble thermoplastic polyamide resin component of the crepingadhesive comprises a reaction product of a polyalkylene polyamine, asaturated aliphatic dibasic carboxylic acid, and a poly(oxyethylene)diamine. The polyalkylene polyamine component has the formula

    NH.sub.2 (C.sub.n H.sub.2n HN).sub.x H

wherein n and x are each integers of 2 or more. The aliphatic dibasiccarboxylic acid component has the formula

    HOOC--R--COOH

wherein "R" is a divalent aliphatic radical having from 1 to 8 carbonatoms. The poly(oxyethylene) diamine component has the formula ##STR1##wherein "a" is 1 or 2, "b" is from 5 to 50, and "c" is 1 or 2.Preferably, "a+c" averages about 2.5 and "b" averages about 8.5.

An essential characteristic of the resins of this invention is that theyare phase-compatible with the polyvinyl alcohol, i.e., they do notphase-separate in the presence of aqueous polyvinyl alcohol.

In another aspect, the invention resides in a method for crepingcellulosic webs comprising (a) applying to a rotating creping cylinderan aqueous admixture containing from about 90 to about 99.95 weightpercent water and from about 0.05 to about 10 weight percent solids,wherein from about 20 to about 90 weight percent of said solids iswater-soluble polyvinyl alcohol and wherein from about 10 to about 80weight percent of said solids is a water-soluble, thermoplasticpolyamide resin which is phase-compatible with the polyvinyl alcohol,said polyamide resin comprising the water-soluble thermoplastic reactionproduct of a polyalkylene polyamine, a saturated aliphatic dibasiccarboxylic acid, and a poly(oxyethylene) diamine; (b) pressing acellulosic web against the creping cylinder to effect adhesion of theweb to the surface of the cylinder; and (c) dislodging the web from thecreping cylinder by contact with a doctor blade. Preferably, the aqueousadmixture contains from about 0.1 to about 1.0 weight percent solids.

The invention will be described in greater detail with respect to thespecific examples set forth below.

DESCRIPTION OF THE PREFERRED EMBODIMENT Example 1: Preparation ofPolyamide Resin

83 grams (0.8 mole) of diethylene triamine, 146 grams (1.0 mole) ofadipic acid, and 180 grams (0.3 mole) of a poly(oxyethylene) diamine(Jeffamine ED 600 manufactured by Texaco Chemical Co. and having theformula described above with "a+c" averaging 2.5 and "b" averaging 8.5)were added to a three-neck resin flask equipped with a mechanicalstirrer, thermometer, and a water trap. The solution was heated to 160°C. and water collected over 105 minutes as the temperature rose to 195°C. The total amount of water collected was 30 ml (83.4% of theoretical).The contents of the flask were poured into a pan and cooled, solidifyinginto a yellow mass having a waxy feel. On standing the solid appeared toabsorb water from the air to give a very tacky surface feel. A 2%solution of the product in distilled water at 20° C. had a specificviscosity of 0.19.

Example 2: Preparation of Creping Adhesive

A 5 weight percent aqueous solution of the polyamide prepared in Example1 was combined with a 5 weight percent aqueous solution of a polyvinylalcohol (PVA) having a weight average molecular weight of about 120,000and a degree of hydrolysis of about 86%. The polyamide solution and thePVA solution were combined in various solids weight ratios ofPVA/polyamide of from 90/10 to 30/70, respectively. No phase separationwas observed in these blends.

Example 3: Water Uptake (Wettability)

Thin films of a 74/26 PVA/polyamide resin blend made as described above(this invention), and a thermosetting polyamide resin (control) wereprepared by casting 5 weight percent solution into a silicone rubbermold at room temperature and allowing the water to evaporate. Theresultant films, which were about 8 mils in thickness, were cut intostrips of about 1×5 inches and "cured" in an oven at 200° F. for 15minutes. After cooling to room temperature, the film strip was weighedto determine its dry weight. The film sample was then immersed in waterat 72° F. for a time of 10, 30, 50, or 90 seconds. The sample wasremoved from the water on a wire mesh, shaken to remove surface drops ofwater, and weighed to determine the wet weight. The results are setforth in TABLE I.

                  TABLE I                                                         ______________________________________                                        Water Uptake Rates                                                                         Wet Weight/Dry Weight Ratio                                      Time (Seconds) Control  This Invention                                        ______________________________________                                         0             1.0      1.0                                                   10             1.47     1.80                                                  30             1.68     1.94                                                  50             1.72     2.40                                                  90             2.01     2.68                                                  ______________________________________                                    

As the results illustrate, the thermoplastic films of this inventiontake up water to a greater extent and at a greater rate than thethermosetting polyamide resin (control).

Example 3: Production of Facial Tissue

Facial tissue was made under controlled laboratory conditions using twodifferent creping adhesives: a 0.1 weight percent solids solution of ablend of PVA and the thermoplastic polyamide of Example 1 in a 74/26ratio of PVA to polyamide (this invention); and a 0.1 weight percentsolids solution of a blend of PVA and a thermosetting polyamide resin inthe same ratio (control).

The resulting tissues were tested for softness by a trained sensorypanel which, on a 1 to 10 scale, rated the softness of the tissues madein accordance with the method of this invention at 7.2 compared to 6.8for the control, illustrating improved creping performance.

The same tissue samples were also evaluated for stiffness using amechanical device which measures the force required to crush a sample toa fixed degree. Measured crush loads were 53.9 grams for the samplesmade in accordance with this invention versus 64.7 grams for thecontrol, illustrating that the tissues made in accordance with thisinvention were less stiff.

The foregoing examples illustrate the improved wettability of thethermoplastic polyamide creping adhesives of this invention and theutility of the method of this invention for making creped tissueproducts.

I claim:
 1. A method of creping cellulosic webs comprising: (a) applyingto a rotating creping cylinder an aqueous admixture containing fromabout 90 to about 99.95 weight percent water and from about 0.05 toabout 10 weight percent solids, wherein from about 20 to about 90 weightpercent of said solids is water-soluble polyvinyl alcohol and whereinfrom about 10 to about 80 weight percent of said solids is awater-soluble, thermoplastic polyamide resin which is phase-compatiblewith the polyvinyl alcohol, said polyamide resin comprising the reactionproduct of a polyalkylene polyamine, a saturated aliphatic dibasiccarboxylic acid, and a poly(oxyethylene) diamine; (b) pressing acellulosic web against the creping cylinder to effect adhesion of theweb to the surface of the cylinder; and (c) dislodging the web from thecreping cylinder by contact with a doctor blade.
 2. The method of claim1 wherein the poly(oxyethylene) diamine has the following formula:##STR2## wherein "a" and "c" are each 1 or 2 and "b" is from 5 to
 50. 3.The method of claim 2 wherein the polyalkylene polyamine has thefollowing formula:

    NH.sub.2 (C.sub.n H.sub.2n HN).sub.x H

wherein "n" and "x" are each integers of 2 or more.
 4. The method ofclaim 3 wherein the saturated aliphatic dibasic carboxylic acid has theformula:

    HOOC--R--COOH

wherein "R" is a divalent aliphatic radical having from 1 to 8 carbonatoms.
 5. The method of claim 1 wherein the poly(oxyethylene) diaminehas the formula: ##STR3## wherein "a" and "c" are each 1 or 2 and "b"has an average value of about 8.5.
 6. The method of claim 5 wherein thepolyalkylene polyamine is diethylene triamine and the saturatedaliphatic dibasic carboxylic acid is adipic acid.
 7. The method of claim6 wherein the amount of water-soluble thermoplastic polyamide is about25 weight percent of the solids.